A. Field of the Invention
This invention relates generally to the field of devices used to measure and display bio-potential signals generated by the body. More particularly, the invention relates to a wireless, remotely programmable electrode transceiver assembly that sends electromyography (EMG) signals via wireless transmission to a base unit. The base unit obtains a patient""s EMG signal from the wireless transceiver and supplies the signal to a monitor unit for display.
B. Statement of Related Art
Electromyography is technique by which electrical activity associated with functioning skeletal muscle is converted to a perceptible, usually visual, record. The technique is used to help diagnose certain neuromuscular disorders, such as Parkinson""s disease, and in biofeedback training.
EMG equipment has heretofore typically taken the form of one or more electrodes that are attached to the patient""s skin adjacent to the skeletal muscle of interest, an EMG display monitor, and a set of wires connecting the electrodes to the monitor. Some tests, such as Parkinson disease tests, can require more than 10 sensors, each with four wire lines. The wires coupling the electrodes to the monitor limit patient mobility, increase the amount of time needed to set the patient up for the EMG acquisition, and can restrict or prevent the patient from engaging in many types of motions or exercises during the acquisition of the EMG signal (e.g., walking, running, rowing machine, etc.).
Wireless medical monitoring and diagnosis systems have been proposed in the prior art. U.S. Pat. No. 5,862,803 to Besson et al. describes a wireless electrode/sensor patch system with sensor, controller and transceiver electronics contained in an electrode patch assembly. U.S. Pat. Nos. 5,307,818, 5,168,814 and 4,981,141, all issued to Segalowitz, describe a wireless electrode system for electrocardiogram (ECG) monitoring. The Besson et al. and Segalowitz patents are incorporated by reference herein.
The Segalowitz patents describe a single piece electrode patch with built-in microchips for wireless one way communication and a snap on electronic-assembly that fastens to a disposable electrode patch. However, the electrode patch is a special two-conductor type that is not conventional. The electrode assemblies are either transmit only or receive only (not both). A reference signal is transmitted from the base unit to only the Right Leg electrode patch, which is receive only. Electrodes can only be programmed via manual switches on the electrode casing, not over-the-air from the base unit. For the multiple electrode embodiment, the base unit contains multiple receivers and antennas which imply multiple transmit frequencies are required for the system and over-the-air signaling (thus making the base unit more costly to implement). There is no mention of error correction or detection capability in the electrodes or base unit.
In another embodiment of the Segalowitz ""818 patent, there is discussion of a single strip assembly which contains all of the electrodes required for 12-lead ECG monitoring with microchip circuitry contained in the strip assembly (not in the individual electrode patches). In this configuration, the ECG signals from each electrode are multiplexed and transmitted from a single transmitter contained in the strip assembly via time multiplexing on a single digitally encoded frequency channel. However, no time multiplexing on a single frequency channel is discussed for their multiple transmit electrode embodiment.
The present invention provides a self-contained device that can acquire an EMG signal, in the form of voltage level, from the surface of the skin. The EMG signal is digitized and sent to a base station using wireless technology. Multiple wireless EMG signals in accordance with the invention can be used on the patient, such as in a 10 electrode Parkinson disease EMG test. Because the system is a wireless system, the problems enumerated above associated with wires leading from the electrode to the monitor are avoided.
A wireless biopotential sensor includes an adhesive strip having a lower surface for placement against the skin of a patient and an upper surface. A pair of conductive electrodes are applied to the lower surface of the adhesive strip. A sensor substrate is applied to the upper surface. The sensor substrate includes first and second conductive contact pads that are placed in registry with the pair of conductive electrodes, with the contact pads arranged in electrical contact with the conductive electrodes. An electronics module is applied to the sensor substrate and arranged in electrical contact with the contact pads. The electronics module comprises a power supply and electronics for generating a wireless signal containing biopotential signals detected by the pair of conductive electrodes.
In another aspect, a wireless electromyography acquisition system is provided. The system includes a plurality of individual, remotely programmable sensors each having a wireless transceiver. Each of the sensors includes a patch electrode adapted to be placed on the surface of the patient""s body for measuring electrical potentials from skeletal muscle. The system further includes a base unit comprising a wireless transceiver for sending and receiving messages to the plurality of individual wireless transceivers. The electrodes include circuitry for converting received EMG signals into digital form.
Each of the wireless electrodes includes a means for encoding unique identification information associated with the wireless electrodes, such as manufacturer serial number and user-selected identification codes. An analog to digital converter and microcontroller computing platform are included in the sensor and provide a means for converting the digital form of the EMG signals into packets and for appending the encoded identification information to the packets. A buffer is provided for storing EMG digital data containing the encoded identification information prior to transmission by the electrode""s transceiver to the base unit.
Time division multiplexing is a preferred way by which the multiple EMG electrodes transmit wireless data to the base unit. The base unit transmits a global time base signal to the individual wireless transceivers. The global time base signal is used for synchronizing the timing of transmission of signals acquired by the individual wireless electrodes to the base unit in discrete time slots in a single frequency channel. This time division multiplexing provides that each wireless transceiver transmits its signals to the base unit in discrete time slots, with the wireless transceivers sharing a common channel.
The base unit has an interface to an EMG monitor for display and analysis by the user. Preferably, the EMG monitor is a conventional, standard monitor typically used today in the hospital setting. The EMG signals are provided by the base unit to the monitor in a fashion that is transparent to the monitor, i.e., the data is formatted and provided in a form whereby the monitor cannot distinguish the signals from conventional, wired electrode input signals.
These and still other aspects and features of the invention will be more apparent from the following detailed description of a presently preferred embodiment.